CoPy/C催化剂应用碱性介质氧还原催化的电化学性能

利用碳黑（Vulcan XC-72R）中加入硫酸钴和吡啶（Py）作为催化剂前驱体,经溶剂分散热处理构建了一类新型的高效氧还原CoPy/C复合催化剂.并运用循环伏安法（CV）和旋转圆盘电极（RDE）技术研究了不同Co含量的CoPy/C催化剂在碱性介质中对氧还原的电催化活性.结果表明:Co的存在对氧的催化剂活性位的形成有重要影响,800℃下所制备的10%Co30%Py/C（质量分数）复合催化剂表现出最佳的氧还原催化活性.以其制备的气体扩散电极在3.0 mol·L^-1KOH电解质溶液（O₂气氛）中0.014 V（相对于标准氧电极（RHE））即可产生明显的氧还原电流.同40%Py/C相比,10%Co30%Py/C催化氧还原的起峰电位正移了71 mV,同时表现出明显的极限扩散电流.在-0.16 V时电流密度达到最大值,电流密度为1.0 mA·cm^-2,半波电位在-0.07 V.透射电镜分析表明所制备的碳黑载吡啶钴（10%Co30%Py/C）催化剂平均粒径为20 nm.     

Au@Pt纳米粒子催化O2还原反应的电化学研究

以100 nm的Au粒子为核,抗坏血酸为还原剂,H2PtCl6·6H2O为前驱体,合成了Pt包Au核壳结构纳米粒子( Au@ Pt)及其修饰的玻碳(GC)电极(Au@ Pt/GC).采用旋转圆盘电极等常规电化学方法,比较了Au@ Pt/GC和商用碳载铂(Pt/C)修饰的玻碳电极(Pt/C/GC)催化O2还原反应活性及耐甲醇性能,发现Au@ Pt纳米粒子在铂用量很低的情况下,其催化O2还原反应活性仍与商用Pt/C相当,而且还具有优良的耐甲醇性能;其催化O2还原反应机理按O2直接还原成H2O的四电子历程进行.     

Dealloyed Silver Nanoparticles as Efficient Catalyst Towards Oxygen Reduction in Alkaline Solution

Silver nanoparticles(Ag NPs) were prepared by dealloying Mg-Ag alloy precursor. The obtained Ag NPs have an average ligament size of (50±10) nm. Electrocatalytic activity of Ag NPs towards oxygen reduction reaction(ORR) in 0.1 mol/L NaOH solution was assessed via cyclic voltammetry(CV), rotating ring disk elec-trode(RRDE) techniques, and electrochemical impedance spectroscopy(EIS). The electrochemical active area for the ORR was evaluated by means of the charge of the underpotential deposition(UPD) of lead(Pb) on Ag NPs. The CV results indicate that Ag NPs have a higher current density and more positive onset potential than the bulk Ag electrode. RRDE was employed to determine kinetic parameters for O₂ reduction. Ag NPs exhibit a higher kinetic current density of 25.84 mA/cm² and a rate constant of 5.45×10^-2 cm/s at -0.35 V vs. Hg/HgO. The number of electrons(n) involved in ORR is close to 4. Further, EIS data show significantly low charge transfer resistances on the Ag NPs electrode. The results indicate that the prepared Ag NPs have a high activity and are promising catalyst for ORR in alkaline solution.     

Pt/C催化剂氧还原反应的交流阻抗动态研究

本文通过RDE和EIS联合技术、等效电路模型,研究了酸性体系中商业Pt/C催化剂ORR行为. 研究发现Pt/C动态界面包括两个彼此独立的过程：1）Pt表面原有PtO还原至Pt过程,2）ORR促进新PtO形成过程,为催化材料稳定性及活化性提供了关键依据;并发现动态界面促进多孔电极重构以及与传输匹配过程.在高过电位下,ORR的高反应速率可通过增加催化材料憎水性予以改善. 上述研究结果可对ORR的直流电化学研究进行有效补充,并提供建模基础.     

Preparation and Characterization of Pt/Co‐Core Au‐Shell Magnetic Nanoparticles

Pt/Co‐core Au‐shell nanoparticles were synthesized via a two‐step route using NaBH₄ as a reducing agent. The nanoparticles are characterized by UV‐vis spectroscopy, transmission electron microscopy (TEM) and powder X‐ray diffraction (XRD). The results indicate that the as‐synthesized Pt/Co‐core Au‐shell nanoparticles have a disordered face centered cubic (fcc) structure, whereas the annealed Pt/Co‐core Au‐shell nanoparticles exhibit an ordered face centered tetragonal (fct) structure. Superconducting quantum interference device (SQUID) studies reveal that the coercivity of the annealed Pt/Co‐core Au‐shell nanoparticles increases to 510 Oe after heat treatment at 500 °C for 2 h.     

Core–Shell Pd@M (M=Ni,Cu, Co) Nanoparticles/Graphene Ensembles with High Mass Electrocatalytic Activity Toward the Oxygen Reduction Reaction

Herein, it is demonstrated that pyrene butyric acid (PBA)-stabilized metal nanoparticles with core–shell morphology, Pd@M_NPs (M=Ni, Cu, Co), non-covalently supported on graphene (G) sheets, are more active towards oxygen electroreduction in alkaline environments than the benchmark Pd/C catalyst, albeit with a 70 % lower precious metal loading. The PBA-stabilized Pd@M_NPs (M=Ni, Cu, Co)/G ensembles were prepared by employing a simple modified polyol method and galvanic replacement and thoroughly characterized with advanced microscopy imaging and complementary spectroscopic techniques. Electrochemical studies revealed that Pd@Ni_NPs/G presents the optimum performance, exhibiting a 30 mV more positive onset potential and 3.2 times greater mass activity over Pd/C. Moreover, chronoamperometric assays showed the minimum activity loss for Pd@Ni_NPs/G, not only among its core–shell counterparts but importantly when compared with the benchmark catalyst. The excellent performance of Pd@Ni_NPs/G was attributed to the (a) presence of PBA as stabilizer, (b) uniform Pd@Ni_NPs dispersion onto the graphene sheets, (c) efficient intra-ensemble interactions between the two species, (d) existence of the core–shell structure for Pd@Ni_NPs, and (e) stability of the Ni core metal under the reaction conditions. Last, the oxygen reduction on Pd@Ni_NPs/graphene occurs by the direct four-electron reduction pathway, showing great potential for use in energy related applications.     

脉冲微波辅助化学还原合成Pt/C 催化剂及其电催化氧还原性能

采用脉冲微波辅助化学还原法制备了质子交换膜燃料电池(PEMFC)用Pt/C 催化剂. 通过透射电镜(TEM)和X射线衍射(XRD)等分析技术对催化剂的微观结构和形貌进行了表征, 并利用循环伏安(CV)、线性扫描(LSV)和恒电位测量等方法评价了催化剂催化氧还原性能. 在此基础上制备了膜电极(MEA)并组装成单电池, 考察了制备的Pt/C 催化剂作为阴极催化剂材料的电催化性能. 结果表明, 脉冲微波辅助化学还原法是一种制备PEMFC催化剂的有效方法, 溶液pH值和微波功率对Pt 颗粒直径和分散有重要影响. TEM和XRD结果显示, 当溶液pH值为10 且微波功率为2 kW时, Pt 纳米粒子较均匀地分散在碳载体上, 粒径分布在1.3-2.4 nm之间, 平均粒径为1.8 nm. CV、LSV和恒电位测试结果表明, 该催化剂电化学比表面积(ESA)为55.6 m²·g^-1, 具有良好的催化氧还原反应活性和稳定性. 单电池测试结果表明, 在溶液pH值为10条件下, 微波功率为2 kW时制备的催化剂作阴极催化剂时, 单电池最高功率密度为2.26 W·cm^-2·mg^-1, 高于微波功率为1 kW时的最高功率密度(2.15 W·cm^-2·mg^-1)和Johnson Matthey催化剂的最高功率密度(1.89 W·cm^-2·mg^-1).     

石墨烯载Pt纳米粒子的原位还原制备及氧还原电催化性能

采用改进的化学氧化还原法(Hummers法)氧化鳞片石墨, 再超声振荡剥离得到氧化石墨烯(GO)水溶液. 通过聚二烯丙基二甲基氯化铵(PDDA)分子对GO表面功能化, 由于带正电荷的PDDA分子功能化的GO与带负电荷的^2-离子间的静电作用, 使Pt离子组装到GO表面, 再通过原位还原被束缚的Pt离子, 同时GO被还原成石墨烯片(GNs), 得Pt/PDDA-GNs催化剂. 相对空白GNs负载的Pt纳米粒子和商业化Pt/C(JM), Pt/PDDA-GNs催化剂有较高的氧还原活性和稳定性. 前者可归因于Pt颗粒尺寸细小和分散度较高, 后者是由于PDDA分子与Pt原子间的电子作用及对Pt颗粒的钉扎作用, 从而减缓了Pt的氧化和迁移.     

Ir-skinned Ir-Cu Nanoparticles with Enhanced Activity for Oxygen Reduction Reaction

The development of methanol-tolerate oxygen reduction reaction(ORR) electrocatalysts is of special significance to direct methanol fuel cells system. Iridium is known for its better methanol tolerance than platinum and able to survive in harsh acidic environment. However, its activity is relatively low and thus the approach to improve Ir's ORR is desired. Herein, bimetallic Ir-Cu nanoparticles(NPs) with controllable Ir/Cu compositions(ca. 1:2 to 4:1, atomic ratio) are synthesized via a galvanic replacement-based chemical method. The as-synthesized Ir-Cu NPs are investigated as ORR catalysts after electrochemically leaching out the surface Cu and forming Ir-skinned structures. Around 2- to 3-fold enhancement in the intrinsic activity has been observed in these Ir-skinned Ir-Cu catalysts compared to Ir counterpart. The approach is demonstrated to be a promising way to prepare efficient Ir ORR catalysts and lower catalyst cost.     

铁铂核壳纳米粒子修饰玻碳电极制备及对亚硝酸盐还原的电催化性能

通过循环伏安法（CV）在玻碳（GC）电极表面电沉积出分布较为均匀的纳米Fe粒子,制得纳米Fe粒子修饰的GC（纳米Fe/GC）电极,再经“电荷置换”制得具有Fe核Pt壳结构的纳米粒子修饰的（纳米PtFe/GC）电极。 SEM结果显示,纳米Fe/GC和纳米PtFe/GC表面粒子的形貌均呈立方体形,分布较为均匀,粒径在60 nm左右。 纳米PtFe/GC电极对亚硝酸盐的还原具有很高的电催化活性。 3种电极的电催化活性顺序依次为：纳米Fe/GC＜纳米Pt/GC＜纳米PtFe/GC。 相对于纳米Pt/GC电极,纳米PtFe/GC电极的起始还原电位（Ei）正移了0.14 V,还原峰电流（ip）增大了3倍。     

交替微波加热法对制备氧还原催化剂性能的影响

详细研究了交替微波加热法制备多壁碳纳米管负载Pt催化剂(Pt/MWCNTs)的过程中交替微波加热(5s-on/5s-off)次数对催化剂性能的影响.X射线粉末衍射(XRD)结果表明,Pt的晶粒尺寸在开始的加热阶段基本上没有发生变化,但是随着加热次数的增多,Pt的晶粒尺寸逐步增大.采用循环伏安法和旋转圆盘电极技术考察了催化剂的电化学活性.结果显示,以5s-on/5s-off加热20次时,催化剂显示出最佳的催化活性;在0.5mol· L-1 H2SO4饱和氧水溶液中催化剂的氧还原起峰电位接近1.0 V(vs RHE).交替微波加热法简单经济,在大批量制备催化剂等纳米材料方面显示出较好的应用前景.     

A Simple Electrochemical Approach Based on Inexpensive Wall‐Jet Screen‐Printed Ring Disk Electrode to Evaluate Oxygen Reduction Catalysts

A simple electrochemical approach to evaluate oxygen reduction catalysts using an inexpensive screen‐printed ring disk carbon electrode system, consisting of a ring electrode deposited with MnO₂ and a disk electrode modified with the catalysts for study, is developed in this study. The as‐prepared MnO₂ is selective and sensitive for H₂O₂ oxidation in the presence of O₂ and is crucial to the proposed approach. By coupling with a wall‐jet electrochemical cell, the product generated from the reduction reaction at the disk electrode can effectively be monitored at the MnO₂‐deposited ring electrode. Model catalysts of nano‐Au and nano‐Pd representing 2e^? reduction of O₂ to H₂O₂ and 4e^? reduction to H₂O, respectively, were evaluated as electrode materials in oxygen reduction reaction to demonstrate the applicability of the proposed method.     

Graphene Supported Platinum Nanoparticles as Catalyst for Oxygen Reduction Reaction

Graphene supported Pt nanoparticles were fabricated via electrochemical reduction method and the application of them in oxygen reduction reaction was also investigated. The results of field emission scanning electron microscope(SEM), X-ray photoelectron spectroscopy(XPS) and Raman spectroscopy reveal that the interaction between Pt nanoparticles and graphene sheets can prevent graphene from agglomeration and improve the electronic conductivity of the composite. And the graphene supported Pt nanoparticles exhibit excellent electrocatalytic activity toward oxygen reduction reaction.     

A Chemical Dealloying Approach for Pt Surface-enriched Pt3Co Alloy Nanoparticles as Oxygen Reduction Reaction Electrocatalysts

Pt-based alloys are the optimal electrocatalysts for oxygen reduction reaction(ORR) currently. Dealloying of Pt-based alloys has shown to be an effective approach to improving ORR activity. Electrochemical dealloying is controllable for morphology by changing electrochemical parameters but is difficult to scale up due to complex operation and energy consumption. Chemical dealloying is suitable for a large scale but it is not easy to control the morphology because highly corrosive acids(HNO₃ or H₂SO₄) are commonly used. In this work, a facile chemical dealloying method for Pt₃Co/C has been employed to synthesize elec-trocatalysts for ORR using weak acids and buffer solutions of different pH, which could slow down the dissolution rate for Co atoms and increase the diffusion time for Pt atoms to improve ORR activity. It can be observed that the mass activities(MA) of the Pt₃Co/C alloy after dealloying with H₃PO₄ and NaH₂PO₄/Na₂HPO₄ buffer solution of pH=6 are close to that after electrochemical dealloying process, and are more than two times that of commercial Pt/C. In addition, Pt₃Co/C after dealloying with a buffer solution of pH=6 only showed a slight degradation in the half-wave potential and electrochemical surface area(ECSA) after stability test for 5000 cycles, which is more stable than commercial Pt/C. It shows that by controlling pH of the solvent, the ORR activity can be further increased. This facile approach provides a new strategy to control morphology of Pt-based electrocatalysts by chemical dealloying, which can contribute to promising application for cathodic electrocatalysts design of proton exchange membrane fuel cells (PEMFCs).     

Electrocatalytic Reduction and Determination of Dissolved Oxygen at a Preanodized Screen‐Printed Carbon Electrode Modified with Palladium Nanoparticles

Efficient and stable electrocatalytic activity for the reduction of O₂ at activated screen‐printed carbon electrodes modified with palladium nanoparticles (SPE*‐Pd) was demonstrated in this study. X‐ray photoelectron spectroscopy confirmed the formation of >C?O functional group on electrode surface during the preanodization procedure at 2.0 V (vs. Ag/AgCl). The existence of chloride moieties was also identified possibly from the organic binder of carbon ink used in SPE fabrication. Both >C?O and chloride functional groups were essential for the excellent stability of the SPE*‐Pd. Electrochemical impedance spectroscopy verified the enhanced kinetic rate of oxygen reduction reaction at the as‐prepared Pd nanoparticles. The SPE*‐Pd showed ca. 250 mV positive shift in peak potential together with twice increase in peak current compared to those observed at a SPE‐Pt. The calibration plot was linear up to 8 ppm of DO with sensitivity and regression coefficient of 4.49 μA/ppm and 0.9936, respectively. The variation coefficient of i_pc for 7 DO determinations with O₂‐saturated pH 7.4 PBS was 2.1%. Real sample assays for ground and tap waters gave consistent values to those measured by a commercial dissolved oxygen meter.     

Pd/Pt二元合金电极的制备及氧还原性能

本文利用欠电位沉积亚单层的Cu及Pt置换取代Cu的方法, 制备了具有不同表面元素组成的Pd/Pt二元合金电极(用Pd/Ptx表示, x指欠电位沉积Cu-Pt置换取代Cu过程的次数),并对其表面元素组成、氧还原性能进行了表征. 在控制欠电位沉积Cu的下限电位恒定(0.34 V)的前提下, 表面Pt/Pd的元素组成比通过重复欠电位沉积Cu及Pt置换取代Cu的次数(1~5次)来可控地调变. 光电子能谱(XPS) 以及红外光谱实验表明,Pd/Ptx电极表层区的Pt：Pd元素组成比随着Pt沉积次数增加而增加, 对Pd/Pt4电极, 在电极表层区约2~3 nm内的Pt/Pd的原子比大约是1:4,而最表层裸露Pd原子的比例仍在20%以上。循环伏安结果显示, 随着Pt沉积次数的增加(1-5次), Pd/Ptx电极表面越不易被氧化。氧还原测试结果显示随着Pt沉积次数的增加(1~4次), Pd/Ptx二元金属电极的氧还原活性依次增加, 经过第3次沉积后其氧还原活性已优于纯Pt,而经4次以上沉积,其氧还原活性基本不变。在其它反应条件相同条件的前提下, Pd/Pt4电极上氧还原的半波电位与纯Pt相比右移约25 mV。结合本文与文献的实验结果,我们初步认为Pd/Ptx二元金属体系氧还原性能改善主要源自表层Pd原子导致其邻近的Pt原子上含氧物种吸附能的降低.     

石墨烯负载Pt催化剂的制备及催化氧还原性能

采用直接化学还原法, 以金属钠为还原剂, 四氯乙烯为碳源, 在石蜡油中不经氧化石墨(GO)和氧化石墨烯(GrO)而直接制备石墨烯(Gr), 然后将Pt纳米粒子担载在Gr基体上, 得到Pt/Gr催化剂, 并对其催化氧还原(OR)性能进行了研究. 通过X射线衍射(XRD), 透射电镜(TEM)和电化学测试对合成催化剂的结构、形貌和电化学性质进行了表征. 实验结果表明: 所制备的Pt/Gr催化剂具有较好的分散性, 平均粒径为3.1 nm; 氧还原起始电位比商业JM-Pt/C催化电极正移了24 mV; 交换电流密度达到1×10^-3 mA·cm^-2, 是商业JM-Pt/C催化电极的2.5倍.     

壳层厚度可调控的Ag@Pd@Pt纳米粒子的合成和甲酸电催化研究

在本课题组研究55 nm Au@Pd@Pt对甲酸电催化效果基础上,我们采用Ag取代Au制备55 nm Ag@Pd@Pt纳米粒子以降低催化剂的成本,并对甲酸的电催化行为进行研究. 研究表明：少量Pt的存在可大幅度提高催化剂的活性,当Pt的覆盖度为0.5 单原子层（ML）时,起始氧化电位最为靠前,氧化峰电流最大,这与Au@Pd@Pt纳米粒子对甲酸电催化行为类似. 与Au@Pd@Pt纳米粒子相比,其最佳起始氧化电位偏正0.05 V,但电催化活性并没有明显的降低. 通过改变催化剂比表面积研究甲酸的电催化行为,发现将9 nm Ag纳米粒子作为内核的9 nm Ag@Pd@Pt负载在活性炭中,在保持催化活性不变的情况下,碳载的催化剂价格可比55 nm Au@Pd@Pt纳米粒子降低220倍左右.     

Electrochemical Design of Ultrathin Palladium Coated Gold Nanoparticles as Nanostructured Catalyst for Amperometric Detection of Formaldehyde

An underpotential deposition (UPD) replacement tactic was employed to design a Pd overlayer on gold (Au) nanoparticles electrodeposited on a carbon ionic liquid electrode (CILE). Pd/Au/CILE was applied as an amperometric sensor for the determination of formaldehyde in aqueous solutions. The sensor displayed two linear ranges from 15 µM–1.4 mM and 1.4–56.7 mM of formaldehyde. The limit of detection was 3 µM of formaldehyde and the sensitivity of the sensor was 2.35 µA mM^?1, using the calibration graph in the lower range. The presence of 20 mM of formic acid and methanol and 10 mM ethanol did not interfere with the determination of formaldehyde solution.